The present invention is directed towards a video line rate converter. More particularly, the present invention is directed towards a method and apparatus for converting an input video signal having a first number of lines (e.g. 625) into an output signal having a second different number of lines (e.g. 525).
One simple method for achieving the desired conversion is to delete a number of input lines equal to the difference in the number of lines in the input and output video signals. The primary drawback of this method (referred to hereinafter as the truncation method) is that significant input information is lost during the conversion process.
Another possible method for achieving the desired conversion is to use an interpolation method wherein all of the input video information is used to generate the output video signal. By way of a simple example, if the conversion ratio is 2/1, each line of the output video signal can be generated by averaging two associated lines of the input video signal. Thus, lines 1 and 2 of the input video signal can be averaged to produce line 1 of the output video signal; lines 3 and 4 of the input video signal can be averaged to generate line 2 of the output video signal, etc.
While the foregoing method is clearly preferable to the truncation method, it would appear to require a relatively large memory to achieve the desired conversion. A straightforward approach would require that the converter store an entire odd and an entire even field of a single input frame and then utilize a predetermined algorithm to perform the interpolation from the number of lines in the input frame to the number of lines in the output frame. This is undesirable, in terms of hardware requirements (a large memory and associated control circuitry is required).